"I am having problems in attatching a file with mails."
The most common reason why users face this problem is that the size of the file that they are trying to attach or download is too big. The limit of the size of attachments is 10 MB.
Another factor which causes a problem is a poor network connection to the internet.
If your attachments are fairly large and you have a poor network connection to the internet, then the attachments will take a very long time to get attached or downloaded. This delay will result in a time-out and you will not be able to attach/download the attachment.
You could ensure that your attachments do not exceed the size limit. If your internet connection is a problem, you could contact your provider.